(1) Field of the Invention
This invention relates to aircraft control surfaces and more particularly to a means of inhibiting uncontrolled flutter of a control surface when a hydraulic pressure failure occurs.
(2) Description of the Prior Art
Most modern jet transport aircraft assure adequate communication between the pilot and the control surfaces to overcome problems such as control surface jams or component failures. This is conventionally accomplished by redundancies in the control system. Unfortunately, flutter prevention demands an even higher standard with respect to each of the individual control surfaces. To overcome the potential danger of flutter the surfaces must be able to cope with failures in combination, such as the concurrent loss of two hydraulic systems, the loss of one hydraulic system plus a structural disconnect at the remaining operable actuator, and in remote cases, the structural disconnect of more than one actuator, assuming the control surface has only two actuators and one is a redundant unit.
A variety of techniques have been utilized to satisfy the higher standard of reliability associated with flutter prevention in control surfaces such as ailerons, rudders and elevators. Typical approaches include the use of nose weights for balance, multiple redundancy of hydraulic supplies or actuators, and the use of actuators with dampers incorporated in their structure. Though such devices add to the weight and life cycle cost of the aircraft, the superior position of the flight controls in the flight safety hierachy has historically prescribed the use of such apparatus to overcome the problem of control surface flutter.